A medical container for filling blood, medicament or the like is demanded not only to be, needless to say, hygienic but also to have high heat resistance capable of enduring sterilization treatment at a high temperature, transparency to enable the check of mingling of a foreign material or visual inspection of the change by blending of a medicament, impact resistance sufficiently high to prevent the bag from rupturing at falling on handling or at packaging and transportation, flexibility for facilitating the discharge of contents, and blocking resistance not to readily cause separation of film or sheet at the production of a medical container or not to contact a medicament-containing medical container with its outer packaging bag.
In particular, demands are increasing for a medical container which can be sterilized at a high temperature of 121° C. or more having a strong sterilization power, can satisfy all of heat resistance, transparency, impact resistance, flexibility and blocking resistance, and can be industrially produced.
For the medical container, a soft polyvinyl chloride, a polyethylene-base material such as high-pressure low-density polyethylene, linear low-density polyethylene, high-density polyethylene and ethylene-vinyl acetate copolymer, and a polypropylene-base material such as propylene homopolymer and random or block copolymer of propylene and other α-olefin have been heretofore used.
The vinyl chloride-base resin is excellent in the balance of heat resistance, transparency, flexibility and impact resistance but this resin has a problem in that a plasticizer used for imparting the performance dissolves out into a medicament solution or food.
Out of polyethylene-base materials, the high-pressure low-density polyethylene is deficient in that the heat resistance or impact strength is poor. As for the linear low-density polyethylene, a polyethylene having a low density is used so as to enhance the transparency or flexibility, but when the density is decreased, insufficient heat resistance is liable to result and furthermore, problems arise, for example, the low molecular weight component of the resin lowers the blocking resistance of the container or dissolves out into a medicament. The ethylene-vinyl acetate copolymer is excellent in the transparency but disadvantageously low in the heat resistance. The high-density polyethylene is deficient in that the transparency and impact resistance are poor. Thus, polyethylene-base materials cannot satisfy a good balance of heat resistance, transparency and impact resistance.
Out of polypropylene-base materials, the propylene homopolymer and propylene random copolymer are excellent in the transparency but inferior in the blocking resistance, and the propylene block copolymer is poor in the balance of flexibility, impact resistance and transparency.
For solving these problems, with respect to the medical container using a polyethylene-base material, a multilayer container having a layer mainly comprising a high-density polyethylene and a layer mainly comprising a linear low-density polyethylene has been proposed (see, for example, JP-A-5-293160 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
Furthermore, a polyethylene-base material produced by using a metallocene-base catalyst and having excellent impact resistance and transparency has been recently developed and studies are being made to apply this material to a medical container. Also, a method of using these materials in combination and stacking two, three or more layers has been proposed (see, for example, JP-A-7-125738).
On the other hand, with respect to the medical container using a polypropylene-base material, a technique of using a resin composition comprising a propylene-base random copolymer having an α-olefin content of 5 to 8 mass % and a mixture of specific ethylene-propylene and ethylene-butene random copolymers to obtain a container excellent in the heat resistance, transparency, impact resistance and the like has been disclosed (see, for example, JP-A-8-231787).
Also, a container having a constitution such that a layer comprising a propylene homopolymer or propylene-α-olefin random copolymer containing from 0 to 30% of a polyethylene-base resin is provided as the outer layer and a three-layer laminate comprising a mixture of a propylene homopolymer or a propylene/α-olefin random copolymer and an olefin-base elastomer or the like is provided as the intermediate layer has been proposed (see, for example, JP-A-9-262948).
Furthermore, a technique of using a resin composition comprising a crystalline polypropylene and a propylene/α-olefin copolymer having a specific limiting viscosity ratio, and forming a specific morphology at the thermoformation has been proposed (see, for example, JP-A-10-316810).
However, the container described in JP-A-5-293160 cannot always hold a sufficient transparency after sterilization at a temperature of 121° C. or more and fails in fully satisfying the requirement on the market that sterilization can be performed at a higher temperature in a shorter time.
Also in the case of using the laminate described in JP-A-7-125738, the transparency after high-temperature sterilization of 121° C. or more is not sufficiently high and moreover, the impact resistance is also insufficient to readily cause rupture at the heat-welded part on falling of the container, therefore, improvements are demanded. Furthermore, a film or sheet obtained by a water cooling inflation method, a T-die method or the like has particularly a smooth surface and readily causes blocking of films or sheets with each other and when these are pulled apart, a whitened flaw remains on the surface and the outer appearance is seriously deteriorated in some cases.
The resin composition described in JP-A-8-231787 has a problem that the heat resistance and transparency are still insufficient.
The container described in JP-A-9-262948 does not have a sufficiently high impact resistance and particularly, in the case of a container having a volume of 1 L or more, the impact resistance is not satisfied from the standpoint of preventing rupture on falling.
The method described in JP-A-10-316810 has a problem in that not only the impact resistance or the thermal shrinkage percentage at the heat sterilization expresses strong anisotropy due to orientation of the domain but also stable production while keeping the quality can be hardly attained because the formation of specific morphology is sensitive to the molding conditions or the like.
The present invention has been made under these circumstances and an object of the present invention is to provide a medical container having heat resistance high enough to enable sterilization at a temperature of 121° C. or more and exhibiting excellent properties in all of the transparency, impact resistance, flexibility and blocking resistance.